Is it petty to ask for $5 back from a friend?

A friend and I went out to eat. The place only took cash and she asked to borrow $5. I lent it to her.

A month has gone by, and she seems to forgot about it. I know it's not intentional because she is a good friend and has a job.

I plan on asking it back tonight when I come over. Is it petty?
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